The use of stents, stent grafts, occluders, filters and other implantable medical devices introduced endoluminally for treating a damaged or diseased area of a patient is well known. With many such devices it is necessary to fix the device within a lumen of a patient in such a manner that it can be assured that the implantable medical device will remain in position throughout its period of use, in some cases substantially indefinitely. It is also important to be able to fix the device in position while this is being deployed, typically by being expanded from a contracted configuration for insertion into a patient. For this purpose, it is well known to provide barbs on such devices. These are typically pin-like projections fitted to the implantable medical device, which projections in use extend outwardly of the device so as to penetrate the walls of the lumen in which the device is to be fitted, thereby acting as anchors for anchoring the device in position.
Barbs of this nature can take a variety of forms and have a variety of characteristics in dependence upon the particular requirements for a medical device or medical application. In many instances, the barbs are fixed to a support structure of the implantable medical device, such as a stent. These may be fixed so as to be integral with the support structure, such fixing being provided, for example, by welding a barb to the support structure or by any other suitable fixing. The barbs may be flexible and thus able to be trained to a compressed configuration in which they remain tight against a compressed support structure while on the introducer and able to expand to an operative position extending beyond the perimeter of the support structure of the medical device during deployment. In some instances the barbs or at least a part of the barbs may be substantially rigid.
For the purposes of delivering such a medical device within a patient, it is important to be able to deliver the medical device, with its barbs, endoluminally within a patient, in which case the medical device is typically deliverable by means of a relatively small diameter and flexible introducer. This generally results in the barbs needing to be flexible enough so that they can be pushed against an inner carrier element of the introducer and held in that position by an outer sheath or other holding device to retain the barbs compressed. This invariably places certain limits upon the structure and design of such barbs.
U.S. Pat. No. 5,755,777 discloses an expandable transluminal graft prosthesis for repair of an aneurism which is provided with a plurality of barb elements at the proximal and distal ends of the graft, fixed to internal surfaces of end stents provided at these ends of the prosthesis. When located on an introducer, the end stents act to push the barbs attached thereto inwardly towards a carrier cannula such that the barbs are held spaced from an outer sheath which covers the prosthesis up to the point at which it is to be deployed within a patient.